In general, a vulcanization product of a fluorine-containing elastomer has excellent resistance to heat and oils and, therefore, has been widely utilized in various industrial fields, such as in the fields of automobiles, ships, aircrafts and hydraulic devices and general machine industries, and in the field of devices for the prevention of environmental pollution. Examples of vulcanization products of a fluorine-containing elastomer include O-rings, gaskets, oil seals, diaphragms, hoses, rolls and sheets. Recently, an improvement in productivity and a labor-saving have been earnestly desired in the production of vulcanization products. Accordingly, it has been desired to develop a fluorine-containing elastomer having excellent workability in a vulcanization molding thereof. Particularly, since vulcanization molding of a fluorine-containing elastomer by injection is advantageous from a viewpoint of not only an improvement in productivity but also a labor-saving, the demand for a fluorine-containing elastomer which is suitable for vulcanization molding by injection, has increased.
As mentioned above, a vulcanization product of a fluorine-containing elastomer composition has excellent resistance to heat and oils. However, a fluorine-containing elastomer is generally not satisfactory in mold processability due to the high viscosity thereof as compared to other types of elastomers. In order to improve processability of a fluorine-containing elastomer composition, it has been attempted to lower the molecular weight of the elastomer so as to increase the flowability of the elastomer composition. However, this attempt has been unsuccessful. That is, the obtained elastomer composition is disadvantageous not only in that its workability is poor in roll molding due to occurrence of an unfavorably strong adhesion of the elastomer composition to the roll, but also in that a low molecular weight elastomer is difficult to crosslink by a polyol vulcanization, so that the important properties of vulcanization products, such as compression set resistance, are likely to be unsatisfactory.
Further, when a fluorine-containing elastomer having a low molecular weight is vulcanization molded by injection, the resultant molded product is poor in mold release properties, so that problems arise in working efficiency. In addition, when an elastomer having a low molecular weight is used for producing a molded product having a complicated configuration, the molded product is likely to suffer cracking, breakage and swelling, leading to a lowering of yield and productivity.
In order to improve the processability of fluorine-containing elastomers, it has been proposed to use a processing aid, such as a higher fatty acid ester, a silicone compound and a low molecular weight polyethylene (see, for example, Examined Japanese Patent Application Publication No. 52-44896 corresponding to U.S. Pat. No. 4,065,419). However, when the processing aid is used in a small amount, a satisfactory improvement of processability cannot be achieved. On the other hand, when the processing aid is used in an amount sufficient to improve the processability, the vulcanization molded product becomes very poor in tensile strength and sealability at high temperatures. Further, in order to improve the mold release properties of fluorine-containing elastomers, it has been attempted to use an external mold release agent, and an internal mold release agent, such as a higher fatty acid ester, a silicone compound, a fatty acid amide, or a low molecular weight polyethylene. However, when an internal mold release agent is used in an amount sufficient to improve the mold release properties, the vulcanization molded product becomes very poor in tensile strength and sealability at high temperatures. On the other hand, when an external mold release agent is used, since the effect of the agent to improve mold release properties is lowered as the molding is repeated many times, it is disadvantageously necessary to repeatedly coat the agent on the surface of a mold and, in addition, a trace of the external mold release agent is likely to remain on the surface of the molded product, so that the molded product is of no commercial value.
In the above context, studies have been made in order to solve the above-mentioned problems.
For example, there has been proposed a method in which N,N,N',N'-tetrasubstituted 1,8-diaminonaphthalene is incorporated in a fluorine-containing elastomer composition (see Examined Japanese Patent Application Publication No.2-50140 corresponding to U.S. Pat. No. 4,529,759), a method in which a perfluoropolyether having a brominated terminal group is added to a fluorine-containing elastomer composition (see Unexamined Japanese Patent Application Laid-Open Specification No. 62-143951 corresponding to U.S. Pat. No. 5,061,759), a method in which a telomer of or a cotelomer of a vinylidene fluoride, each having bromine or iodine at a terminal thereof, is added to a fluorine-containing elastomer composition (see Unexamined Japanese Patent Application Laid-Open Specification No. 63-92664 corresponding to European Patent Publication No. 251285), and a method in which an alkyl cellosolve is added to a fluorine-containing elastomer composition (see Unexamined Japanese Patent Application Laid-Open Specification No. 63-189450). However, such additives are either special chemicals and therefore expensive, or highly inflammable liquids, so that the practical use of these additives on a commercial scale has been limited.
Further, in Examined Japanese Patent Application Publication No. 57-8124, there is disclosed a method in which an amine or a salt thereof as a vulcanizing additive is added to an aqueous emulsion of a fluorine-containing copolymer at a coagulation thereof. However, this method pertains to a diamine vulcanization method and, therefore, satisfactory results cannot be obtained with respect to the processability thereof in a vulcanization molding and to the properties of the vulcanization product obtained.